1. Field of the Invention
The present invention relates to a semiconductor light emitting device and a method for producing the same. Specifically, the present invention relates to a semiconductor light emitting device wherein a nitride semiconductor layer is provided on a silicon substrate (Si substrate) as a light emitting layer, and a method for producing the same.
2. Description of the Related Art
Usually, in a light emitting device using a nitride semiconductor material, such as GaN, InN, AlN, or a mixed crystal thereof, a nitride semiconductor film, e.g., an InxGa1xe2x88x92xN crystal layer, is provided on a sapphire substrate as a light emitting layer.
However, in recent years, a silicon (Si) substrate which is less expensive than a sapphire substrate and which has a larger area than that of the sapphire substrate has been used. When using such a Si substrate as a substitute for a sapphire substrate, a less expensive nitride semiconductor light emitting device can be produced.
In the case where a nitride semiconductor light emitting device is produced using a Si substrate, if the temperature of a nitride semiconductor film is decreased to room temperature after epitaxial growth has been performed at a high temperature, the nitride semiconductor film shrinks considerably in comparison to the Si substrate due to a difference in the thermal expansion coefficient between the Si substrate and the nitride semiconductor film, the nitride semiconductor film having a larger thermal expansion coefficient than that of the Si substrate.
FIG. 8 is a schematic diagram showing a structure of a nitride semiconductor light emitting device using a Si substrate. As shown in FIG. 8, if the temperature of a nitride semiconductor film 32 is decreased to room temperature after the nitride semiconductor film 32 has epitaxially grown over a Si substrate 31 at a high temperature, the nitride semiconductor film 32 shrinks considerably. This shrinkage causes tensile stress at the interface of the Si substrate 31 and the nitride semiconductor film 32. As a result, cracks 33 may be formed in both the nitride semiconductor film and the Si substrate as shown in FIG. 8.
When such cracks 33 are formed in a nitride semiconductor light emitting device having a double heterostructure, the amount of leak current, which does not contribute to the emission of light, is increased. As a result, the semiconductor light emitting device cannot emit light with high brightness.
According to one aspect of the present invention, a semiconductor light emitting device includes: a silicon substrate; and a plurality of column-shaped multilayered structures formed on the silicon substrate in such a manner that the column-shaped multilayered structures are insulated from one another, the column-shaped multilayered structures being made of a nitride semiconductor material, and each column-shaped multilayered structure including a light emitting layer, wherein the column-shaped multilayered structures are connected to one another by an electrode.
In one embodiment of the present invention, an insulating film is provided on the silicon substrate for insulating the column-shaped multilayered structures from one another.
In another embodiment of the present invention, the column-shaped multilayered structures are arranged with an interval of 5-20 xcexcm therebetween.
In still another embodiment of the present invention, the column-shaped multilayered structures are arranged in a matrix along a  less than 11-2 greater than  crystal direction and a direction orthogonal to the  less than 11-2 greater than  crystal direction over the silicon substrate.
In still another embodiment of the present invention, a cross-section of each column-shaped multilayered structure has the shape of a square or a rectangle.
In still another embodiment of the present invention, a cross-section of each column-shaped multilayered structure has the shape of a triangle.
In still another embodiment of the present invention, the length of each column-shaped multilayered structure along a direction orthogonal to the  less than 11-2 greater than  crystal direction of the silicon substrate is 100 xcexcm or smaller.
In still another embodiment of the present invention, the electrode which connects the column-shaped multilayered structures to one another is a transparent electrode which allows transmission of light emitted by the column-shaped multilayered structures through the transparent electrode.
In still another embodiment of the present invention, the electrode which connects the column-shaped multilayered structures to one another is provided with a bonding electrode for supplying an external electric current to the electrode.
In still another embodiment of the present invention, the column-shaped multilayered structures emit light having the same wavelength.
In still another embodiment of the present invention, light emitted by each of the column-shaped multilayered structures has any of a plurality of predetermined different wavelengths.
In still another embodiment of the present invention, adjacent column-shaped multilayered structures are electrically connected by a conductor.
According to another aspect of the present invention, a method for producing a semiconductor light emitting device includes steps of: providing an insulating film having a plurality of opening portions on a silicon substrate; forming column-shaped multilayered structures of a nitride semiconductor material in the opening portions of the insulating film, each column-shaped multilayered structure including a light emitting layer; and forming an electrode for electrically connecting the column-shaped multilayered structures to one another.
Thus, the invention described herein makes possible the advantages of providing a nitride semiconductor light emitting device which has a long effective lifetime and which emits light with a high brightness, and a production method thereof.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.